BS EN 1006-2009 pdf download.Advanced technical ceramics Monolithic ceramics Guidance on the selection of test pieces for the evaluation of properties.
The basis of any inspection of any material or batch of manufactured units is to obtain sound information on their fitness for purpose (quality). Advanced technical ceramics are diverse in material, format and application as are the methods devised to test their fitness for purpose. Before arranging any inspection or testing scheme it is wise to consider in depth the nature of the material, its final format in relation to test-pieces required for tests, the accuracy of test methods and the failure criticality in its application.
NOTE It is not the purpose of this European standard to define criteria for fitness for purpose. This is subject to agreement between parties.
3.2 Material homogeneity and anisotropy
3.2.1 Most advanced technical ceramic materials are made by powder technology processes involving the formation of a rigidized powder mass (e.g. pressing, slip casting, etc.) before subjecting this to a densification process (e.g. sintering. reaction bonding, hot pressing). The homogeneity and isotropy of the rigidized powder mass and the control imposed during the subsequent densification process can exert a considerable influence on the homogeneity of the final densified product. Consequently, attributes can vary from one place to another within a component or between components of the same batch.
3.2.2 One of the principal sources of a variation of attributes is density, arising from inhomogeneity of unfired (green) density, which has a subsequent significant effect on many mechanical poperties. Large localised variations in unfired density are usually manifest as excessive distortion in firing, porous regions, or cracking. Other varying attributes are grain size (usually resulting from varying heat treatment conditions between components) and chemical composition (usually resulting from inhomogeneous interaction between initial powder particles or between particles and the atmosphere, perhaps involving the migration of species).
3.2.3 Material inhomogeneity is most prevalent in large components or blocks of material, or in components requiring special firing conditions, It is frequently met with during material development, but is usually minimised during commercial product development.
Material anisotropy is sometimes encountered in materials which have some form of directional microstructure. This may result, for example, from a combination of the initial powder particle shape and the rigidizing process to make a green shape, or during firing if uniaxial hot pressing is employed Attributes subsequently determined can be dependent on the direction in which a test-plece is cut and in which the property or characteristic is determined.
3.3 Test method accuracy
3.3.1 Most test methods specifically developed for advanced technical ceramics have associated with them a possible uncertainty of result determined by the accuracy of individual contributions from each parameter involved in the measurement. The potential uncertainties arising shall be taken into account when examining the consistency of a parameter within a batch of units or between batches, or examining whether it meets a given specification level.
3.3.2 It should be noted that in cases where the scatter of results of a test is similar to or less than that attributable to the accuracy of test method, the test is clearly unable to distinguish between individual test-pieces or samples. An improvement of the accuracy level of the chosen test or an alternative test method should be sought.
3.3.3 Certain tests for advanced technical ceramics produce a wide scatter of results as a consequence, for example, of the influence of occasional flaws or other defects. e.g. a strength test or dielectric breakdown test. The results from such tests shall be treated statistically (see e.g. EN 843-5 for strength tests), and the confidence level of the mean result or other parameters should be calculated such that the degree of discrimination between results from different batches, or between a set of results and a specification value, is clearly understood.
3.4 Sampling schemes for individual manufactured items
3.4.1 Sampling schemes are conventionally divided into those for inspection by attributes, e.g. ISO
2859-1, or by variables, e.g. ISO 3951 (all parts).
NOTE See the Bibiograpliy foe- these and other ISO standards on statisbcs
The selection of an appropriate scheme should be subject to agreement between parties.
3.4.2 Inspection by attributes consists of examining a sampled unit and deciding whether or not it achieves an appropriate criterion. A decision on the fitness for purpose of a batch is by counting the number of non-achieving units in the batch sample. An example might be the presence of cracks (see EN 623-1) or surface blisters in an as-fired ceramic component. Sampling plans for inspection by attributes are given in ISO 2859-1.
3.4.3 Inspection by variables involves the measurement of a property or properties using a recognised test method producing numerical values for each unit In the sample.BS EN 1006-2009 pdf download.
BS EN 1006-2009 pdf download
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